The Baltimore Longitudinal Study of Aging is a long-term, multidisciplinary, comprehensive study of aging. The study in men was initiated in 1958; in women in 1978. Studies include clinical, physiological, genetic, psychological, and behavioral variables. The history of the study is one of periodic (every two years) testing of a group of "core" variables with shorter term specific studies which have been periodically introduced into the study and completed. No conclusion to the study is contemplated since it provides a cadre of human volunteers covering the entire adult age range who are available for the introduction of cutting-edge research proposals as new clinical research procedures become available.